diff --git a/src/hamming.rs b/src/hamming.rs
new file mode 100644
index 0000000..04d77b7
--- /dev/null
+++ b/src/hamming.rs
@@ -0,0 +1,19 @@
+/// Return the Hamming distance between the strings,
+/// or None if the lengths are mismatched.
+pub fn hamming_distance(s1: &str, s2: &str) -> Option<usize> {
+    if s1.len() != s2.len() {
+        return None;
+    }
+
+    if s1.is_empty() || s2 == s1 {
+        return Some(0);
+    }
+
+    let mut count = 0;
+    for (key, ch) in s1.chars().enumerate() {
+        if s2.as_bytes()[key] != ch as u8 {
+            count += 1;
+        }
+    }
+    Some(count)
+}
diff --git a/src/lib.rs b/src/lib.rs
index 5617c52..f997ddc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -23,6 +23,7 @@ pub mod fizzy;
 pub mod sublist;
 pub mod anagram;
 pub mod acronym;
+pub mod hamming;
 pub mod luhn_from;
 pub mod allergies;
 pub mod luhn_trait;
diff --git a/tests/hamming/mod.rs b/tests/hamming/mod.rs
new file mode 100644
index 0000000..5dd5241
--- /dev/null
+++ b/tests/hamming/mod.rs
@@ -0,0 +1,78 @@
+use exercism::hamming;
+
+fn process_distance_case(strand_pair: [&str; 2], expected_distance: Option<usize>) {
+    assert_eq!(
+        hamming::hamming_distance(strand_pair[0], strand_pair[1]),
+        expected_distance
+    );
+}
+#[test]
+fn empty_strands() {
+    process_distance_case(["", ""], Some(0));
+}
+#[test]
+#[ignore]
+/// disallow first strand longer
+fn disallow_first_strand_longer() {
+    process_distance_case(["AATG", "AAA"], None);
+}
+#[test]
+#[ignore]
+/// disallow second strand longer
+fn disallow_second_strand_longer() {
+    process_distance_case(["ATA", "AGTG"], None);
+}
+#[test]
+#[ignore]
+fn first_string_is_longer() {
+    process_distance_case(["AAA", "AA"], None);
+}
+#[test]
+#[ignore]
+fn second_string_is_longer() {
+    process_distance_case(["A", "AA"], None);
+}
+#[test]
+#[ignore]
+/// single letter identical strands
+fn single_letter_identical_strands() {
+    process_distance_case(["A", "A"], Some(0));
+}
+#[test]
+#[ignore]
+/// small distance
+fn single_letter_different_strands() {
+    process_distance_case(["G", "T"], Some(1));
+}
+#[test]
+#[ignore]
+/// long identical strands
+fn long_identical_strands() {
+    process_distance_case(["GGACTGAAATCTG", "GGACTGAAATCTG"], Some(0));
+}
+#[test]
+#[ignore]
+fn no_difference_between_identical_strands() {
+    process_distance_case(["GGACTGA", "GGACTGA"], Some(0));
+}
+#[test]
+#[ignore]
+fn complete_hamming_distance_in_small_strand() {
+    process_distance_case(["ACT", "GGA"], Some(3));
+}
+#[test]
+#[ignore]
+fn small_hamming_distance_in_the_middle_somewhere() {
+    process_distance_case(["GGACG", "GGTCG"], Some(1));
+}
+#[test]
+#[ignore]
+fn larger_distance() {
+    process_distance_case(["ACCAGGG", "ACTATGG"], Some(2));
+}
+#[test]
+#[ignore]
+/// large distance in off-by-one strand
+fn long_different_strands() {
+    process_distance_case(["GGACGGATTCTG", "AGGACGGATTCT"], Some(9));
+}
diff --git a/tests/libtest.rs b/tests/libtest.rs
index 9024343..8214e6a 100644
--- a/tests/libtest.rs
+++ b/tests/libtest.rs
@@ -38,3 +38,4 @@ mod binary_search;
 mod spiral_matrix;
 mod allergies;
 mod nucleotide_count;
+mod hamming;